Excel Formula issue

I am using Excel 2016. I am creating a birthday spreadsheet. I have an Age column in which the formula is calculated upon the current date which is cell J1 and the date of birth which is column D. My formula is in column E (Age) and is calculated as  =DATEDIF(D39,$J$1,"y")&" years"  which in this cell will show the age once D39 birth date is entered. Every function I try shows False or #Name? How can I get the cells in column E to show a blank until I enter the date of birth in cell D39?